Various systems for the gasification of solid or heavy liquid fuels are known for the conversion of such fuels into fuel gases or light hydrocarbon liquids. Conventionally, the raw fuel gases produced require complex, energy consuming, and toxic waste producing processing in order to produce a clean gas for use in commercial equipment.
Systems which use the gasification of a biomass, or combustible plant material, such as wood, wood scrap, wood trimmings, leaves, wood waste, paper scrap, and the like, have been proposed since the fuel gas (biogas) produced is low in sulfur content relative to other fuels. This permits the fuel gas produced from such a biomass to be combusted as a fuel with only the removal of solid particulate matter therefrom. Conventionally, such systemss have proposed to clean the fuel gas by cooling the same in a heat exchanger and then filtering the gas. The heat exchanger and the filter are both likely to foul with tars and carbon carried in the fuel gas so that they would require frequent replacement. An example of an arrangement of a gasifier for electricity generation is described in "Appendix C, State of the Art in Biomass Conversions" of the report; Evaluation of Biomass Systems for Electricity Generation AP-2265, EPRI Research Project 1348-7, Final Report, February 1982, prepared by Battelle, Columbus Laboratories. In a gasification described therein, the Omnifuel gasifier converts wood wastes in a sand fluidized bed into low BTU gas. In that system, the product gas is passed through cyclones to remove solid particulate matter, through a heat exchanger, and then through a scrubber, before being used to generate electricity. The use of a scrubber in such a system poses a problem of disposal of the scrubber effluent which may contain toxic constituents.
As aforementioned, a fuel gas (biogas), produced by gasification of a biomass, is low in sulfur content and would permit combustion of such a gas with only particulate removal, provided the temperature of the biogas is reduced to levels tolerable by combustion turbines. For such conventional commercial turbines, those temperatures are in the 260.degree.-555.degree. C. range.
It is an object of the present invention to provide a process for producing electric power using a biogas producing system as a source of fuel for an electric power producing turbine, which does not require complex, energy consuming, and toxic liquid waste-producing processing of the biogas prior to its use as the fuel.